An electric-operated fuel injector for a compression-ignition internal combustion engine may comprise an intensifier piston for creating a high pressure injection of fuel directly into an associated engine cylinder. An intensifier piston comprises a head of given end area exposed to a control fluid, oil for example, in a control chamber, and a plunger, or rod, of smaller end area exposed to liquid fuel in an injection chamber.
It is known to employ an electric-operated spool valve for controlling both the introduction of pressurized control fluid into the control chamber and the draining of control fluid from the control chamber. As control fluid is introduced under pressure through one portion of the spool valve into the control chamber, the intensifier piston is downstroked to cause fuel in the injection chamber to be injected under pressure from a nozzle of the fuel injector into an associated engine cylinder. The intensifier piston is effective to amplify the pressure of the control fluid by a factor equal to the ratio of the head end area to the plunger end area and cause the amplified pressure to be applied to liquid fuel in the injection chamber. As a result, fuel is injected into a combustion chamber at a pressure substantially greater than the pressure of the control fluid. After an injection, the spool valve is operated to allow oil to drain from the control chamber through another portion of the spool valve, and the intensifier piston is upstroked to re-charge the injection chamber with liquid fuel in preparation for the next injection.
Examples of fuel injectors having valves like those just described appear in U.S. Pat. Nos. 3,837,324; 5,460,329; 5,479,901; and 5,597,118.
It is believed that as those fuel injectors operate, there is some degree of interaction between the supplying of control fluid to, and the draining of control fluid from, the control chamber. In other words, it is believed that those patents do not contemplate a fuel injector for an engine, the fuel injector comprising a body, a variable volume injection chamber within the body, a fuel port at which fuel enters the body, a fuel passage for conveying fuel from the fuel port to the injection chamber, a fuel injection port at which fuel from the injection chamber is injected from the body, a variable volume control chamber, a control fluid supply port at which control fluid enters the body, a control fluid drain port at which control fluid drains from the body, a piston operatively relating the injection chamber and the control chamber such that the volume of the injection chamber varies inversely with the volume of the control chamber, a control fluid supply port at which control fluid enters the body, a supply passage for conveying control fluid from the supply port to the control chamber, an electric-operated supply valve comprising an electric supply valve actuator and a supply valve mechanism controlled by the electric supply valve actuator for selectively controlling flow of control fluid through the supply passage, and a drain passage for conveying control fluid from the control chamber to the drain port, an electric-operated drain valve comprising an electric drain valve actuator and a drain valve mechanism controlled by the electric drain valve actuator for selectively controlling flow of control fluid through the drain passage, each valve actuator being selectively operable independent of the other to selectively operate the respective valve mechanism independent of the other, and the supply and drain passages being mutually independent such that fluid flow through each is independent of fluid flow through the other.